The present invention concerns an endoprosthesis that can be percutaneously implanted by means of a catheter in a patient's body, especially inside a blood vessel or other body cavity The endoprosthesis is oblong and hollow. It can be expanded, once properly implanted, to fit the lumen of the vessel or cavity.
Percutaneously implanted expanding endoprostheses are known. They are employed to open or dilate blood vessels. There are two major forms. One is compressed before implantation and allowed to expand resiliently to its original size once implanted. The other is slender and implanted unstressed and stretched with a balloon catheter once implanted.
The endoprosthesis described in European A 0 183 372 is accommodated on a balloon catheter and expanded and accordingly released into the blood vessel. This prosthesis constitutes a stent in the form of a flexible cylinder produced by knitting, crocheting, or other reticulating process from filaments of a tissue-compatible metal or plastic. The individual meshes comprise loosely connected loops. As the balloon inflates, the meshes deform plasticly and the prosthesis expands permanently.
Stents that expand automatically are known from European A 0 183 372 and U.S. Pat. No. 4,732,152. These prostheses are elastic. They are radially compressed before implantation and implanted in that state in the patient's body. Once the prosthesis is in place, the compression is eliminated and the device expands until it rests snug in the vessel or body cavity.
The endoprosthesis described in European A 0 183 372 is radially compressed before implantation and advanced in that state by a plunger through a catheter previously inserted into the vessel until the desired location is attained. Advancing the prosthesis through the catheter requires considerable force due to the considerable friction between the two devices.
The endoprosthesis described in U.S. Pat. No. 4,732,152 is woven and elastic. It is maintained compressed by a continuous double sleeve at the distal end. The sleeve is stripped from the compressed prosthesis like a sock from a foot. The concomitant friction can be decreased by liquid between the two halves of the sleeve. Although the decreased friction originally makes this approach look very elegant, it is very difficult to maneuver.
WO 93 121 985 A1 discloses a balloon catheter with an invariable lumen for angioplasties. The balloon is surrounded by another balloon containing a drug for treating the inner surface of the vessel or body cavity. The outer balloon is porous. The outside of the inner balloon demarcates in conjunction with the inner surface of the outer balloon an accommodation for the drug, which is delivered through a length of flexible tubing. How much of the drug penetrates the wall of the outer balloon extensively depends on the pressure inside the inner balloon. A lot of drug will be released, no matter how much is needed, when the inner balloon expands considerably in executing the angioplasty. The pressure of the emerging drug can actually damage the inner surface of the vessel when the outer balloon rests directly against it. It is impossible to control the dose independent of the expansion of the inner balloon.